1. Field of the Invention
The present invention relates to a lens system, an image pickup system, and a drive control method for the lens system, which are configured to control drive of movable optical members including a zoom lens, focus lens, and iris by a command apparatus. In particular, the present invention relates to a lens system, an image pickup system, and a drive control method for the lens system, which are used for television broadcast.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2005-328496 describes a conventional control system for movable optical members including a zoom lens and focus lens in a television lens. In the system configuration, a zoom demand as a command apparatus for outputting a command signal for zoom drive and a focus demand as a command apparatus for outputting a command signal for focus drive are connected to a lens body. In addition, as command apparatus that can be connected to the lens body, there are multiple command apparatus including a command apparatus for outputting a stop command, and a command apparatus for controlling an image stabilization optical system.
In addition, the lens body and the command apparatus are connected through cable connection using connectors. The connector described in Japanese Patent Application Laid-Open No. 2005-328496 has a 20-pin structure, and a 20-conductor cable having as many conductors as the number of pins is used for connecting the lens body to the command apparatus. In addition, a cable of approximately 1 m is normally prepared as the cable between the lens body and the command apparatus in order to operate beside the lens body.
FIG. 19 is a block diagram illustrating the conventional television image pickup system described above. A zoom demand 3 for operating a zoom lens of a lens body 2 connected to a camera body 1 can generate a return switch command, a VTR switch command, a shot command, and a shot memory command in addition to a zoom command for zoom drive control. A focus demand 4 for operating a focus lens of the lens body 2 can generate the same switch commands as those in the zoom demand 3 in addition to a focus command for focus drive control. The lens body 2 is connected to the zoom demand 3 and the focus demand 4 by using cables 5 and 6, which are approximately 20-conductor cables normally prepared with a length of approximately 1 m and connecters 7 and 8, respectively.
In the above-mentioned structure, the lens body and each command apparatus are connected via a multi-conductor cable having a length of approximately 1 m. In addition, when connecting multiple command apparatus, it is necessary to use the same number of cables as the multiple command apparatus. Therefore, the following problem arises in a photography site of a broadcasting station.
There may be crane photographing in which a camera and a lens are provided to the tip end of a crane whose length is approximately 3 to 5 meters and command apparatus are operated for photographing by a camera operator at the base of the crane. There may also be photographing of savage animals at a distance from a camera and a lens which are installed in nature. In such cases, the length of the normal cable provided between the lens body and the command apparatus is insufficient, and hence it is necessary to manufacture and install a dedicated extension cable. Therefore, the manufacturing and installation of the dedicated extension cable require cost and time. Cables each including as many as approximately long conductors are installed to correspond to the number of command apparatus, which leads to a problem in that reliability is degraded because there is a risk of damages to conductors and cables when the cables are installed.
Therefore, in order to solve this problem, for example, Japanese Patent Application Laid-Open No. 2008-310093 discloses an optical apparatus that can be easily installed without degrading reliability even in a photography in which the lens body and the command apparatus are distant from each other, by using wireless connection between the lens body and the command apparatus. In addition, Japanese Patent Application Laid-Open No. 2005-328496 discloses the invention that can maintain and improve reliability of wireless data communication even in the case where radio interference or directivity effect occurs due to the use of wireless connection.
However, in the above-mentioned conventional technology disclosed in Japanese Patent Application Laid-Open No. 2008-310093, there is no description about how to deal with a command value after wireless communication is disconnected. Therefore, in the case of a lens apparatus in which the command value is returned to a value at an initial position after the wireless communication is disconnected, the lens is driven to the initial position that is different from the position indicated by the command value so far, and due to this movement of the lens, an unnatural image with a feeling of strangeness is taken.